And although the banks took an average 58 per cent haircut on those loans, some property experts believe Nama still paid above the market value for the properties on which those loans were secured.

Dr Brendan Williams, a lecturer in UCD, who last year co-wrote a major report on Irish ghost estates, said it was "plausible" that Nama could face losses of between 10 and 20 per cent on the loans it had taken over.

This suggests that Nama could have to swallow losses of between €3bn and €6bn unless property prices make a dramatic recovery.

When Nama took over the loans, "the expectation was that the then low market prices were in a distressed market and that Nama should instead pay a higher long-term value for those loans and assets," said Dr Williams.

"This long-term value represented an uplift in price, which Nama expected to realise over seven to 10 years. However, instead of stabilisation and growth, the property markets have deteriorated further since the loans were taken over."

Dr Williams also pointed out that, without knowing the actual value of the properties held by Nama, it was impossible to verify the losses it was facing.

Nama owns 10,000 properties and about 8,000 of these are apartments or duplexes. Nama valued the loans on its books in November 2009 and, since then, domestic house prices in Ireland have fallen by more than 20 per cent.

Apartment prices, which have taken a hammering, have fallen by almost 30 per cent since November 2009.

A spokesman for Nama said the agency had made profits on overseas properties it owns.

"In London and other markets, property prices have risen," protested the spokesman. "Nama has already approved the sale of a number of property assets for more than the agency paid for the linked loans. For example, it made a profit of the sale of loan books associated with the Maybourne Hotel Group."

Gregory Connor, professor of finance with NUI Maynooth, said: "Nama pretends that it can dig itself out of the loss position but that is a bit delusional."

Property developer Paddy McKillen said last week that Nama could lose billions because it lacked the skills to manage valuable assets.

Former HSBC banker Michael Geoghegan has carried out a review into Nama, which suggests changes in how the agency should be run.